1. Field of the Invention
The present invention relates to a tensioner for maintaining constant tension of a non-ended belt, a chain, or the like.
2. Description of the Related Art
A tensioner is a device for maintaining constant tension of a chain, timing belt, or the like that is used, for example, for an engine of an automobile or a motorbike, by pushing or pulling the chain or timing belt in a certain direction if the chain or timing belt becomes loose or slack.
FIG. 18 is an illustration showing an example of a tensioner that is actually installed in the main body of an engine 100. In this engine 100, a non-ending chain 103 encircles a set of two cam sprockets 101 and a crank sprocket 102. The tensioner A has a curve-shaped chain guide 104 that makes contact with the aforementioned timing chain 103 and guides that chain. This chain guide 104 is installed in a free-moving condition with a base portion 105 as a supporting point. Then, by the moving of the chain guide 104 by a retractable and extensible drive shaft 106 of the tensioner A, the tension of the timing chain 103 is adjusted.
FIG. 17(a) shows a conventional tensioner. Such a tensioner A is inserted into a case 51 along with a rotating shaft 52 and a drive shaft 53. The case 51 is to be installed in an apparatus such as an engine, and a flange 51b is formed with an external protrusion in which a hole 51a is formed for the purpose of such installation.
In order to connect the rotating shaft 52 to the drive shaft 53, a male screw portion is formed on the outer surface of the rotating shaft 52 while a female screw portion is formed on the inner surface of the drive shaft 53, and said imposition is done by engaging said screw portions. The rotating shaft 52 and the drive shaft 53, which are connected to each other, are supported inside the case 51 by the back-end portion 52a of the rotating shaft 52 being connected with the case 51 by interfitting said back-end portion 52a with an interfitting hole 59 of the case 51. Also, when the drive shaft 53 is connected with the rotating shaft 52 it is engaged on the front-side part of the rotating shaft 52 to approximately one-half of the overall length of said rotating shaft 52, and a torsion spring 54 is installed at the back-side part of the rotating shaft 52 for the approximately one-half of the overall length of said rotating shaft 52 with which the drive shaft 53 is not engaged.
One end 54a of the torsion spring 54 is fastened onto the rotating shaft 52 from the direction crossing the axial direction while the other end 54b is fastened onto the case 51. Accordingly, when assembled under the condition that the torsion spring is twisted to have a specified torque, the rotating shaft 52 rotates due to the loaded strength of the torsion spring 54.
The drive shaft 53 is in a tube whose cross-section is not circular and into which the approximately front half of the rotating shaft 52 is inserted in the condition of engagement. The part of the drive shaft 53 that engages with the rotating shaft 52 is supported by a bearing 55. This bearing 55 is fixed on the tip part of the case 51.
FIG. 17(b) is a cross-section view of such a bearing 55, and in which in this example has a drive-shaft hole 55a (a hole in which the drive shaft 53 slides while contacting the inner surface thereof) that has a noncircular, approximately oval shape. The peripheral cross-section of the drive shaft 53 has the same shape as the drive-shaft hole 55a, and by inserting said drive shaft 53 into said drive-shaft hole 55a bearing 55 the rotation of the drive shaft 53 is stopped.
In the constitution described above, even if the loaded strength of the torsion spring 54 acts upon the rotating shaft 52 so as to rotate the rotating shaft 52, the drive shaft 53, which is engaged with the rotating shaft 52, does not rotate. Therefore, the loaded strength of the torsion spring 54 that rotates the rotating shaft 52 is converted into the driving force of the drive shaft 53 and the drive shaft 53 moves forward. By this movement, because the drive shaft 53 constantly presses against the timing belt and the chain, they are maintained at a constant level of tension.
In such a structure, on the front-end tip of the aforementioned shaft 53 a cap 56 is installed, and this cap 56 contacts directly or indirectly with the chain or the timing belt as shown in the aforementioned FIG. 17(a). Though not shown in the figures, the back-end portion of the case 51 is sealed by the engagement of a sealing bolt so as to prevent the invasion of dust, water, or other undesired substances. Further, the aforementioned tensioner A is a tensioner of a pushing-type, but a tensioner of a pulling type also is also available.
In the tensioner A of which the structure is described above, if the rotating shaft 52 and the drive shaft 53 are removed from the case 51 by mistake, the initial load previously given to the torsion spring 54 becomes zero, because one end of the torsion spring 54 is fastened on the rotating shaft 52 while the other end is fastened on the case 51, as described above. Accordingly, the reassembly of the rotating shaft 52 and the drive shaft 53 and the reinserting of them into the case 51 is to be done after the torsion spring 54 is wound a specified number of times in order to have an initial load, but sometimes the appropriate number of windings of the torsion spring to have the initial load for such a tensioner is not known. Also, it is extremely difficult to latch both ends of the torsion spring 54 in the condition that the initial load is given as described above.
Also, in the tensioner A, of which the structure is as described above, for converting the rotation torque by the torsion spring 54 into driving force in the axial direction, it is necessary to stop the rotation of the drive shaft 53 by the restraining force of the bearing 55. Therefore, the drive shaft 53, of which the surrounding cross-section shape is formed to be in an approximately oval shape, is inserted into the bearing 55, which has a similar oval-shaped engagement hole, as a result of which the rotation of the drive shaft 53 is stopped, as shown in FIG. 17(b).
However, the problem is that, in order to stop the rotation of the drive shaft, it is necessary to form the cross-section shape thereof into such a noncircular shape as an oval shape, which takes time to do and is troublesome.
Furthermore, the aforementioned bearing 55 is of a plate-shaped member a few millimeters thick, to be manufactured by a press, pattern molding, or the like. The thicker the bearing 55 is, the more steadily the same supports the drive shaft 53 so as to stabilize the operation thereof However, the problem is that, when the bearing 55 is thicker, either the effective stroke length of the drive shaft 53 is forced to be reduced or the storage space of the torsion spring 54 is reduced in the axial direction by the increased thickness.
The present invention is intended to overcome the aforementioned problems, and its purposes are (1) is to provide a drive shaft that enables the initial load of the torsion spring to be retained when the tensioner is removed for maintenance purposes or the like, and also that does not need a bearing to stop the rotation of the drive shaft as is conventionally done, that does not need processing to form the cross-section of the drive shaft to be in a noncircular shape, and does not need to reduce the effective stroke length of the drive shaft or the storage space of the torsion spring; and (2) to provide a tensioner using such a drive shaft.
To attain the aforementioned purposes, the invention set forth in claim 1 is characterized such that it has two shaft portions that compose a set and that are engaged by two screw members, and a spring that has at each of its two ends a hooking portion that is fastened onto one of the aforementioned the two shaft members.
Also, the invention set forth in claim 2 is characterized such that it has two shaft portions composing a set engaged by a screw portion, a spring that has at each of its two ends a hooking portion, each of which is fastened onto one of the aforementioned two shaft members, a case into which the set of the two shaft members and the spring are inserted and that supports one shaft member, and a cap that is supported by the case in the condition of free sliding and that supports the other shaft member. The invention set forth in claim 3 is characterized such that it has two shaft portions composing a set engaged by a screw portion, a spring that has at each of its two ends a hooking portion, each of which is fastened onto one of the aforementioned two shaft members, a case into which the set of the two shaft members and the spring are inserted and that supports one shaft member, with the other shaft member being supported by the aforementioned case in the condition of free sliding. Furthermore, the invention set forth in claim 4 is characterized such that it has a hydraulic system that applies oil pressure, in the same direction as the driving direction of the shaft member, to the load that is input to the aforementioned shaft member.
By the constitution described above, the initial load is maintained when the tensioner is disassembled for maintenance purposes or the like, so that reassembly is made easier. In addition, because the bearing that is typically used in a conventional tensioner is not needed, the assembly of said tensioner is made easier and both hence the number of the personnel work hours needed for assembly and the number of the items needed for assembly can be reduced. Also, extra space in the thickness of the aforementioned bearing that is not needed in this tensioner can be used for the effective stroke length of the drive shaft or for storage space for the torsion spring. Moreover, because a cap slides along the wide contacting surface in the aforementioned case, sliding stability of said cap is improved. Furthermore, the first action of the aforementioned hydraulic system is to perform a buffer action against the high load from the engine.